Modeling and detecting resonant tides of exotic compact objects

Abstract

The event horizon of a black hole in general relativity absorbs all infalling radiation. Any observation of the contrary would immediately challenge the expectation that astrophysical black holes are described by the vacuum Kerr geometry. If a putative black hole does reflect part of the ingoing radiation, its quasi-normal mode structure is drastically altered. Low frequency modes can be introduced that are resonantly excited during the inspiral of a binary system. We study the resulting phase shift of the gravitational wave signal. Building on neutron star results, we obtain a model-independent expression for the phase shift that depends only on quasinormal modes and Love numbers of the compact object. We find that the phase shift is detectable with Einstein Telescope, but by far cannot explore the Planck scale.

Extreme mass-ratio inspirals around a spinning horizonless compact object

“…Therefore for the perfectly reflecting case resonances appear only in the flux at infinity. Equation (52) shows that ω I ω R , which implies that the resonances are typically very narrow and hard to resolve [49,51,52]. The energy flux across a single resonance is very well fitted by a forced harmonic oscillator model [89]…”

“…Finally, note that horizonless compact objects contain lowfrequency modes in their spectrum, which are associated with long-lived quasibound states efficiently confined within the object photon sphere [3,4,21,73]. At variance with the BH case, these low-frequency modes can be excited during a quasicircular inspiral when the orbital frequency equals the QNM frequency, leading to resonances in the fluxes [49][50][51][52]. As discussed in Sec.…”

“…The latter also generically affect the dynamics as well as the quasinormal modes (QNMs) of the central object [3,4,21,48]. The QNM spectrum typically contains lowfrequency modes arising from long-lived, quasibound states, which might be resonantly excited during the inspiral [49][50][51][52]. The role of these resonances in the EMRI dynamics was studied in Ref.…”

“…[51] for a perfectly-reflecting, nonspinning, quasi-Schwarzschild horizonless object, for which an analytical treatment of the problem is possible (see also Ref. [52] for a more recent study). Our framework allows to extend the analysis of Ref.…”

Gravitational-wave constraints on the GWTC-2 events by measuring the tidal deformability and the spin-induced quadrupole moment

“…At very late inspiral regime, the tidal resonance for binary ECO systems is also modeled in Ref. [25], and resonant excitations in ECOs have been constrained via GWTC-1 events [26]. At post-merger regimes for binary ECO, emission of GW echoes following normal inspiral-merger-ringdown signal have been proposed and have been searched [27][28][29].…”